The Yield Loci Curves (YLC's) of compacted cohesive powder specimens, from which its Flow Function (FF) is derived, are frequently described by the Warren Spring equation whose parameters are the cohesion (C), tensile strength (T) and curvature index (n). Ideally, for each pre-consolidation level, T should be determined independently with a special instrument, and C and n extracted from the experimental yield loci measurements by non-linear regression using the Warren Spring equation as a model. There are situations, however, where direct determination of T is not a feasible option, and the number of experimental yield stress data, limited by logistic considerations, can be insufficient for meaningful regression. In such cases, T, C and n can be estimated with a freely downloadable interactive Wolfram Demonstration, with which three (the theoretical minimum) or more experimental yield loci are matched with a generated YLC using the Warren Spring equation as a model. To obtain a match, one moves T, C and n sliders on the screen using the calculated Mean Squared Error (MSE) as a guide and for fine-tuning. At least in principle, once T, C and n have been estimated in this way, they can be used to calculate the corresponding principal stresses and effective internal friction angle. The method is demonstrated with published experimental shear data on wetted glass beads and limestone powder. (C) 2017 Elsevier B.V. All rights reserved.